Is it possible to get pregnant between stopping depo-provera and waiting for the next period?

Yes, if you are outside the normal 12 week time after the injection, you could theoretically become pregnant even if you haven't had a period yet. That is because depo-provera, which is a synthetic progesterone like drug, does not invariably prevent ovulation (egg-release), but does affect sperm penetration into the womb and implantation of an embyo.